Identification of limit sets of a non-ideal system: spherical pendulum-excitation source
We investigate the long-term dynamics of a five-dimensional nonlinear system describing the non-ideal excitation of a spherical pendulum coupled to a limited-power electric motor. By analyzing the phase trajectories y(t) = (y1, y2, y3, y4, y5), we prove several structural theorems regarding the system's limit sets. First, we show that the bilinear combination y1y5 - y2y4 satisfies a closed linear differential equation, which implies its vanishing on every limit set. This leads to a fundamental algebraic identity that holds for all asymptotic states. Furthermore, we establish proportionality relations between the pairs (y1, y4) and (y2, y5) within these sets. We demonstrate that the dynamics restricted to any limit set reduce from the original five-dimensional space to an explicit three-dimensional subsystem parameterized by a single constant K. Finally, for the dissipative regime characterized by C <= -2, we prove the global asymptotic stability of the equilibrium point y* = (0, 0, -F/E, 0, 0), showing that y1^2 + y2^2 + y4^2 + y5^2 tends to zero. These results provide a rigorous basis for the structural description of limit sets and simplify the further analysis of deterministic chaos in pendulum-motor models.